ATX power supply to drive a 12V DC motor?

[Baron]

Basically yes. Yellow is +12V.

Red is the 5V btw.



You may need to draw a bit more current than that for the PSU to
regulate properly but I couldn't give an exact figure. 10 ohms would
only draw 2.5W and I'm sure that won't be enough for the supply to
be comfortable. Best to experiment a bit.

He needs to draw about an amp (1A) for full regulation ! (350W Psu) A
5 or 6 ohm 10 Watt resistor should do it.

FWIW. A number of the old AT Psu machines included a load resistor
that would do this !

 

[Baron]

all yellow wires are 12V
all red ones are 5V
black ones are ground.

inside the powersupply they are all hooked together.

I'd suggest using a bunch of the yellow and black wires to power the
motor (maybe 3 of each)

as graham says sticking some sort of load on the 5V supply may help
but I doubt you motor is real fussy on how well the 12V is
regulated.

Some Psu won't even start up without a load on the 5 volt rail !

 

[Jim Douglas]

Hi,

I have a 12V DC motor (6A under load). The only power supplies I have
around here are ATX. Someone at an electronics shop told me they can be
used to supply the power, but I didn't ask how. Is it just a matter of
using an IDE connector to power the motor?

Regards,

Michael

Check out the latest version of Nut&Bolts where there is an nice article
on using the PS for thngs.

 

[Michael A. Terrell]

Check out the latest version of Nut&Bolts where there is an nice article
on using the PS for thngs.

Nuts & Volts?


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[MK]

Thank you all for your comments and suggestions, they've been most
helpful.

 

[Jim Douglas]

Nuts & Volts?

Yes, and that was not intentional...........

 

[MK]

On second thought, I have further questions (see below) before I buy
the parts. Here is some info about one of the supplies I have:

Model: WIN-400PE
DC: 400W
7.5A/4.5A
AC input (230V 50/60Hz):
+3.3V 15A
+5V 30A
+12V 15A
-5V 0.6A
-12V 0.6A
+5VSB 2A (what is VSB?)
+3.3V & +5V MAX 200W
2.03 (ATX12V standard?)

- Is the 10ohm 10w resister ok, should I go lower (eg. 7ohm 5w)? The
link above states a fix to get a higher voltage by wiring two 1ohm 10w
resistors in series
- Is there an issue with using the PS on/off switch to turn it on and
off? Or, do you recommend I connect the green and black wires to an on
/ off switch (SPDT)?
- Is there a problem with using a small heat sink on the resistor (if I
can find one small enough), rather than heat sink compound?

Regards,

Michael

 

[Arlet]

On second thought, I have further questions (see below) before I buy
the parts. Here is some info about one of the supplies I have:

Model: WIN-400PE
DC: 400W
7.5A/4.5A
AC input (230V 50/60Hz):
+3.3V 15A
+5V 30A
+12V 15A
-5V 0.6A
-12V 0.6A
+5VSB 2A (what is VSB?)

5V stand-by.. used for powering peripherals that can wake up the
computer when there's activity.

+3.3V & +5V MAX 200W
2.03 (ATX12V standard?)

- Is the 10ohm 10w resister ok, should I go lower (eg. 7ohm 5w)? The
link above states a fix to get a higher voltage by wiring two 1ohm 10w
resistors in series

I suggest you experiment with resistors. Some ATX PSUs I've tried
didn't even need a dummy load to function correctly.

- Is there an issue with using the PS on/off switch to turn it on and
off? Or, do you recommend I connect the green and black wires to an on
/ off switch (SPDT)?

Shouldn't matter. If you use the main on/off switch, remember to make a
permanent connection between green/black.

- Is there a problem with using a small heat sink on the resistor (if I
can find one small enough), rather than heat sink compound?

As long as the resistor doesn't get too hot, any method will work. If
you can still touch the resistor after using it for a while, you're OK.

By the way, does your PSU have short-circuit/overload protection ? If
not, I'd put a fuse in there as well, otherwise you risk blowing up the
PSU.. or put a suitable light bulb in series while you're playing
around.

 

[MK]

By the way, does your PSU have short-circuit/overload protection ? If

not, I'd put a fuse in there as well, otherwise you risk blowing up the
PSU.. or put a suitable light bulb in series while you're playing
around.

Thanks for the info. I don't know if it has short-circuit/overload
protection, how can I check this? If it doesn't, will the fuse be wired
to the green and black wires on the large PS connector?

Regards,

Michael

 

[Baron]

Thanks for the info. I don't know if it has short-circuit/overload
protection, how can I check this? If it doesn't, will the fuse be
wired to the green and black wires on the large PS connector?

Regards,

Michael

No! Put a fuse in series with the load, ie your motor!

 

[MK]

I'll be connecting the power supply to a motor speed conroller (the
motor will be connected to the speed controller), so the fuse will be
in series with the controller - is this correct?

Regards,

Michael

 

[Arlet]

Thanks for the info. I don't know if it has short-circuit/overload
protection, how can I check this? If it doesn't, will the fuse be wired
to the green and black wires on the large PS connector?

If it has short circuit protection, the manufacturer will tell you so.
It should be in the instruction booklet (if you have that), or possibly
on the sticker on the outside of the case, or google the model number
on the internet. If you can't find anything, assume it's not protected
against overload/short circuit (many of the older models aren't)

The fuse needs to be connected between the +12V output of the PSU and
the rest of your circuit. Suitable fuses can be found in the automotive
parts section of a local store, if you can't get find them in your
favorite electronics supply store.

 

[Rich Grise]

Ah, something I didn't mention is that I'll be connecting a motor
controller and a counter kit to counter the rotation also. All these can
be powered by 12V, so they may or may not be fussy. Anyone have thoughts
on issues with this setup? For example, I the PSU can manage 11.5V, how
will it affect the kits and motor?

Get a few 12V automotive bulbs, to make dummy loads. Even use one across
the +5 supply - it probably won't light, but will provide a load. You
can either get sockets at the auto parts, RS, or you can solder right
to the bulb bases.

Start the supply by grounding the green lead, as others have said, and
take some measurements.

And please bottom-post.

Good Luck!
Rich

 

[Rich Grise]

Why do you think that? I've never seen anything about this.

Many, many years ago, IBM XT power supplies needed a dummy load or
they wouldn't operate properly - they'd go into overvoltage shutdown,
or whatever the problems they had with 250W switchers in the 1970's.

I don't know if that's still necessary, but I'm so old I only heard
about that green wire a couple years ago. ;-)

So, is the green wire just ON/OFF, or is there a T FF inside the PS?

Thanks,
Rich

 

[Arlet]

Many, many years ago, IBM XT power supplies needed a dummy load or
they wouldn't operate properly - they'd go into overvoltage shutdown,
or whatever the problems they had with 250W switchers in the 1970's.

I don't know if that's still necessary, but I'm so old I only heard
about that green wire a couple years ago. ;-)

So, is the green wire just ON/OFF, or is there a T FF inside the PS?

The green wire is just on/off, the T FF is on the motherboard.

 

[jasen]

So, is the green wire just ON/OFF, or is there a T FF inside the PS?

Just on/off.

The flip-flop that converts the ATX momentary power
switch to a push-button toggle is on the motherboard.

Bye.
Jasen

 

[MK]

I used a different PS than the one I described above. I made the
following modifications:

- green to black
- 10w10ohm resistor on the 5v supply

This supply also has a switch, so I didn't bother connecting an
additional one. I did a quick test to determine whether it works and it
does. I haven't taken measurements, as I've run out of time tonight,
but even so I'm real happy that it works. I still need to buy a fuse
for the short circuit protection also.

Regards,

Michael

 

[MK]

I used a different PS than the one I described above. I made the
following modifications:

- green to black
- 10w10ohm resistor on the 5v supply

This supply also has a switch, so I didn't bother connecting an
additional one. I did a quick test to determine whether it works and it
does. I haven't taken measurements, as I've run out of time tonight,
but even so I'm real happy that it works. I still need to buy a fuse
for the short circuit protection also.

Regards,

Michael

Here are some readings:

+12V supply output is 11.94V
+5V supply output is 5.14V
+3.3V supply output is 3.41V

Regards,

Michael

 

[Lionel]

I'd suggest using a bunch of the yellow and black wires to power the motor
(maybe 3 of each)

Good advice.

as graham says sticking some sort of load on the 5V supply may help
but I doubt you motor is real fussy on how well the 12V is regulated.

PC power supplies don't seem to be as fussy as they used to be about
having a load on the 5V rail. I often use jumpered ATX supplies to run
random devices (including 12V motors) on my bench, & they always fire
straight up - even when the only load is the internal fan (12V).

 

[Lionel]

Regarding a load on the 5V supply. Is this really necessary on the
current ATX power supplies.

Not in my experience.

Isn't there a current standard that states
this should be handled inside the PSU? If this is so, then jumpering
the green and black will be all that is really necessary for a current
ATX PSU to run.

Just jumper it & power it up. If it works, you'll hear the fan start
running. If not, it won't hurt the PSU.